1. Field of the Invention
This invention relates generally to medical devices and procedures, and more particularly to a method and system of deploying stent-grafts in a vascular system.
2. Description of Related Art
Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts formed of biocompatible materials (e.g., Dacron or expanded, porous polytetrafluoroethylene (PTFE) tubing) have been employed to replace or bypass damaged or occluded natural blood vessels.
A graft material supported by a framework is known as a stent-graft or endoluminal graft. In general, the use of stent-grafts for treatment or isolation of vascular aneurysms and vessel walls which have been thinned or thickened by disease (endoluminal repair or exclusion) is well known.
Many stent-grafts, are “self-expanding”, i.e., inserted into the vascular system in a compressed or contracted state, and permitted to expand upon removal of a restraint. Self-expanding stent-grafts typically employ a wire or tube configured (e.g., bent or cut) to provide an outward radial force and employ a suitable elastic material such as stainless steel or Nitinol (nickel-titanium). Nitinol may additionally employ shape memory properties.
The self-expanding stent-graft is typically configured in a tubular shape of a slightly greater diameter than the diameter of the blood vessel in which the stent-graft is intended to be used. In general, stent-grafts are typically deployed through a minimally invasive intraluminal delivery, i.e., cutting through the skin to access a lumen or vasculature or percutaneously via successive dilatation, at a convenient (and less traumatic) entry point, and routing the stent-graft through the lumen to the site where the prosthesis is to be deployed.
Intraluminal deployment in one example is effected using a delivery catheter with coaxial inner tube, it having near its distal end a plunger or stop, and sheath, arranged for relative axial movement. The stent-graft is compressed and disposed within the distal end of the sheath in front of the inner tube stop.
The catheter is then maneuvered, typically routed though a lumen (e.g., vessel), until the end of the catheter (and the stent-graft) is positioned in the vicinity of the intended treatment site. The stop on the inner tube is then held stationary while the sheath of the delivery catheter is withdrawn. The stop prevents the stent-graft from moving back as the sheath is withdrawn.
As the sheath is withdrawn, the stent-graft is gradually exposed from a proximal end to a distal end of the stent-graft, the exposed portion of the stent-graft radially expands so that at least a portion of the expanded portion is in substantially conforming surface contact with a portion of the interior of the lumen, e.g., blood vessel wall.
In straight vessels, placement of the stent-graft is relatively straightforward. However, in complex vessels, e.g., in the aortic arch or other curved vessel, placement of the stent-graft becomes less than ideal.
More particularly, in the aortic arch, the stiffness of the delivery catheter causes the distal tip of the delivery catheter to be positioned closely to the outer radius of curvature of the aortic arch. This positioning of the distal tip of the delivery system combined with the effect of blood flow as the stent-graft is deployed results in a high likelihood for asymmetrical deployment of the stent-graft.
To illustrate, as the stent-graft deployment begins, the blood flow catches the initially deployed springs like the sail of a sail boat and causes some spring and or stent graft portions to bend preferentially in the direction of blood flow to cause uneven deployment such that the portion of the springs or stent graft closer to the inner radius of curvature of the aortic arch bend out from the stent graft and downward when deployed high in the vessel as shown in the example figures. As a result, the proximal end of the stent-graft is not deployed orthogonal to the wall of the aortic arch. To correct the initial asymmetrical deployment, the physician typically repositions the stent-graft, which is generally undesirable depending upon the particular application. Further, due to the repositioning, additional cuff (extender) type stent-grafts may need to be deployed.
The proximal end of the stent-graft is the end closest to the heart whereas the distal end is the end furthest away from the heart as deployed. In contrast and of note, the distal end of the catheter is usually identified to the end that is farthest from the operator (handle) while the proximal end of the catheter is the end nearest the operator (handle). For purposes of clarity of discussion, as used herein, the distal end of the catheter is the end that is farthest from the operator (the end furthest from the handle) while the distal end of the stent-graft is the end nearest the operator (the end nearest the handle), i.e., the distal end of the catheter and the proximal end of the stent-graft are the ends furthest from the handle while the proximal end of the catheter and the distal end of the stent-graft are the ends nearest the handle. However, those of skill in the art will understand that depending upon the access location, the stent-graft and delivery system description may be consistent or opposite in actual usage. When using femoral artery access the distal ends are opposite in the device and catheter, while when using a brachial artery access they are consistent.